Krill are small, shrimp-like crustaceans found throughout the world’s oceans, with particularly large concentrations in the Southern Ocean. These tiny invertebrates, growing up to 6 centimeters (2.4 inches) long, form immense swarms that can be visible from space. The Antarctic krill ( Euphausia superba ) alone is estimated to have a biomass of around 379 million tonnes, making it one of the most abundant animal species on Earth. This vast quantity places krill at the very base of the marine food web, where they transform microscopic plants into a food source for a wide array of larger marine animals.
Diverse Animals That Hunt Krill
A wide variety of marine animals rely on krill as a primary food source, reflecting their abundance and nutritional value across different ocean environments. Baleen whales, known for their immense size, are among the largest consumers of krill. Species like the blue whale, the largest animal on Earth, can consume as much as four tons of krill daily, while humpback whales filter thousands of pounds each day. These whales are found in all oceans, migrating to krill-rich feeding grounds.
Seals are another significant group of krill predators, particularly in the Antarctic. Crabeater seals, for instance, have a diet composed almost entirely of krill, consuming over 63 million tonnes annually. Other seal species, such as leopard seals and fur seals, also include krill in their diets. Over 60 percent of the world’s seal population resides in Antarctica, underscoring the importance of krill to their survival.
Penguins are abundant seabirds in the Antarctic that depend heavily on krill. Many of the 18 different penguin species, including Adélie and chinstrap penguins, primarily feed on krill. These birds are skilled swimmers, capable of catching krill quickly. Fish species also prey on krill, including commercially important fish like cod, pollock, and mackerel, especially during their larval stages. Squid are also significant krill predators, with some Antarctic squid species relying heavily on krill. Seabirds like petrels and albatrosses further diversify the list of krill consumers, often catching krill from the ocean surface.
How Predators Consume Krill
Krill predators employ diverse feeding strategies, ranging from massive filter-feeding to agile individual pursuit. Baleen whales are renowned for their filter-feeding mechanism. They possess specialized baleen plates, which are bristly structures in their mouths. A whale takes in a huge gulp of seawater, then uses its tongue to push the water out through the baleen plates, trapping the krill inside to be swallowed.
Some baleen whales use a unique technique called “bubble-net feeding.” They swim in a spiral, releasing bubbles that form a net around schools of krill, herding them into a dense concentration before lunging upward through the center with their mouths open. This concentrates the prey for efficient consumption. Other whales, like right whales, are “skim-feeders,” swimming through krill swarms with their mouths open, allowing the krill to be filtered by their baleen.
Penguins, in contrast, are active pursuit predators that catch krill individually. They are excellent swimmers, using their powerful flippers to propel themselves through the water. Penguins seize krill with their bills and swallow them whole. Crabeater seals have evolved multilobed teeth that function like a sieve, allowing them to strain krill from the water efficiently. Fish and squid capture krill directly, using their mouths or tentacles to seize the prey.
Krill’s Role in Ecosystems
Krill play a disproportionately large role in marine ecosystems, particularly in the Southern Ocean, where they are considered a foundational species. They serve as the primary link that transfers energy from microscopic phytoplankton to higher trophic levels. Krill consume these tiny plants, effectively packaging this energy into a form digestible by larger animals.
This energy transfer supports a wide array of marine life. Almost all large animals in the Southern Ocean, including whales, seals, penguins, seabirds, and fish, depend on krill for their sustenance. Without krill, the entire Antarctic food web would be severely impacted. Their immense biomass means that over half of the Antarctic krill are consumed by these predators each year.
Threats to Krill and Their Predators
Krill populations, and consequently their predators, face threats from environmental changes and human activities. Climate change is a concern, as ocean warming directly impacts krill growth and distribution. The Antarctic Peninsula, a region with high krill concentrations, is warming, causing krill stocks to shrink and shift southward. This warming also reduces sea ice, which is a habitat for krill, especially for their breeding and feeding on ice algae during winter.
Ocean acidification, a consequence of increased atmospheric carbon dioxide, further jeopardizes krill. Acidification negatively affects the hatching success of krill eggs, with projections suggesting a potential collapse of krill populations.
Commercial fishing for krill, primarily for aquaculture feed, dietary supplements, and human consumption, adds pressure to these vulnerable populations. While the total catch might seem small compared to the overall krill biomass, fishing efforts are often concentrated in specific areas, such as the Antarctic Peninsula’s Area 48, which are important foraging grounds and nurseries for krill and their predators. This localized depletion directly impacts the animals that rely on krill, including penguins and whales, creating competition for food resources.